KR20130062970A - Multi-level inverter and driving method thereof - Google Patents

Abstract

PURPOSE: A multi-level inverter with a DC link switch and an operating method of the same are provided to show multi-level output voltage based on a cell by reducing the number of devices. CONSTITUTION: A multi-level inverter comprises a voltage link part(200) comprising several sub voltage link parts which are connected to several voltage sources to separate the certain voltage source into several voltages, a switching part(210) which generates multi-level voltage based on a switching element, electrically connected to the sub switching part, comprises the sub switching part consisting of several switching elements which are connected to center node, and an inverter part(220) which generates and changes the polarity of multi-level voltage when the switching element of the first group and the second group are operated. The inverter group comprises the switching element of the first and second groups which are connected to the both output ends of the switching part. The center node separates the output ends of the sub voltage link and voltage. [Reference numerals] (230) Control part

Description

Multi-level Inverter and Driving Method Thereof

The present invention relates to a multilevel inverter and a method of driving the inverter, and more particularly, to a multilevel inverter having a DC link switch capable of power factor control and a method of driving the inverter.

Recently, due to the high pressure of industrial equipment, the demand for high voltage inverter system is increasing and renewable energy is getting into the spotlight, so it is possible to control both DC link voltage and AC output phase in solar and fuel cell system. Linked PWM inverters are widely used. At present, much research is being conducted on the topology of multilevel inverters and the topology of grid-connected inverters.

In the case of grid-connected inverters, it is necessary to meet the requirements such as sine output voltage, frequency and power factor, as well as the output current meeting the utility's harmonic current standards. Multi-level inverters have been proposed as an effective way to meet these requirements.

Such a multilevel inverter has the following characteristics. First, as the output voltage level increases, the magnitude of dv / dt and surge voltage generated during switching decreases, and when applied to AC motor driving, the failure due to insulation breakdown of the motor stator winding and damage to the bearing of the motor can be significantly reduced. . It also provides the suppression of the common mode current. Second, since the same output harmonic characteristics can be obtained at a lower switching frequency than a two-level inverter, switching losses can be reduced to increase efficiency. Third, since the voltage applied to the switch is limited to the DC link terminal voltage, it is possible to appropriately set the rated voltage level of the power semiconductor switch by adjusting the number of levels.

1 is a view showing the structure of a multi-level inverter of the general diode clamping method for obtaining a five-level output voltage.

As shown in FIG. 1, a typical diode clamping multilevel inverter is connected back-to-back by sequentially switching to multiple stage taps obtained from a plurality of capacitors connected in series to a single high voltage DC link. This is possible. This is applied to some practical applications of the high-voltage high-capacity inverter system.

However, such a diode-clamping multilevel inverter requires not only a separate control technique to solve the DC link voltage imbalance problem, but it is also difficult to realize a system as the number of levels increases, and an imbalance voltage is applied to the clamping diode. There are problems such as uneven current of the switching elements.

In addition, multilevel inverters inherently require more switching elements than two-level inverters. As the number of parts in the system increases, the reliability and efficiency of the system decreases and the cost increases.

An embodiment of the present invention is to provide a multi-level inverter and a method of driving the inverter that can implement a multi-level output voltage based on the basic cell simply by minimizing the number of devices, and the output voltage level is very easy to expand. There is this.

Another object of the present invention is to provide a multi-level inverter and a method of driving the inverter, in which the switching loss is minimized by performing only the function of polarity conversion for AC output without the PWM control of the bridge-type switching elements constituting the inverter.

Furthermore, it is possible to configure not only single-phase but also three-phase multilevel inverters, and a multilevel inverter capable of providing an arbitrary n-level three-phase output by increasing the number of levels through a module corresponding to each phase and a driving method thereof. There is another purpose in providing.

A multilevel inverter according to an embodiment of the present invention includes a voltage link unit for dividing an input voltage into at least two voltages; A switching unit including a plurality of switching elements connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage, and outputting a multilevel voltage according to driving of the switching elements; And switching elements of the first group and the second group connected to both ends of the switching unit, wherein the complementary operation of the switching element of the first group or the switching element of the second group periodically controls the polarity of the multilevel voltage. It characterized in that it comprises an inverter unit for changing and outputting.

Herein, switching elements adjacent to each other among the switching elements of the switching unit are connected to each other to form a series.

The switching elements of the switching unit are characterized in that the power element of the same characteristics.

The multilevel inverter further includes a control unit for controlling the switching unit and the switching elements of the inverter unit, wherein the control unit generates a control signal using a sine wave signal and a triangular wave signal, and generates the switching elements through the generated control signal. It is characterized by controlling.

In addition, the multi-level inverter according to another embodiment of the present invention includes a voltage link unit including a plurality of sub-voltage link unit connected to each of a plurality of voltage sources to divide the voltage source into a plurality of voltages; A sub-switching unit comprising a plurality of switching elements respectively connected to both ends of each output of the sub-voltage link unit and an intermediate node dividing the voltage, and electrically connected to each other between the sub-switching units adjacent to each other; A switching unit for outputting a multilevel voltage according to the driving of the switching elements; A first group and a second group of switching elements connected to both ends of the output of the switching unit, and periodically complementary to the polarity of the multilevel voltage during complementary operation of the first group of switching elements or the second group of switching elements. It characterized in that it comprises an inverter unit for changing and outputting.

Here, the plurality of switching elements connected to the output ends of the switching unit is characterized in that the adjacent switching elements are connected to each other to form a series.

When the voltage link unit has two sub voltage link units that divide the corresponding voltage into two voltages, the inverter unit outputs a 9 level voltage having different polarities.

In addition, the multi-level inverter according to another embodiment of the present invention includes a first multi-level inverter receiving a first voltage source to convert the first multi-level voltage and outputs; And receive the first voltage source or at least one second voltage source independent of the first voltage source, convert the second multilevel voltage into a second multilevel voltage, and output the second multilevel voltage different from the first multilevel voltage. And a second multilevel inverter for outputting, wherein the first multilevel inverter and the second multilevel inverter include: a voltage link unit for dividing an input voltage into at least two voltages; A switching unit including a plurality of switching elements connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage, and outputting a multilevel voltage according to driving of the switching elements; And switching elements of the first group and the second group connected to both ends of the switching unit, wherein the complementary operation of the switching element of the first group or the switching element of the second group periodically controls the polarity of the multilevel voltage. It characterized in that it comprises an inverter unit for changing and outputting.

Here, at least one of the first multilevel inverter and the second multilevel inverter may include a controller configured to output a multilevel voltage having a different phase according to control of at least one of the switching unit and the inverter unit. do.

According to an embodiment of the present invention, there is provided a method of driving a multilevel inverter, the method comprising: dividing a voltage inputted by a voltage link unit connected to a voltage source into at least two voltages; Outputting a multilevel voltage by driving a plurality of switching elements respectively connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage; And periodically changing polarities of the multilevel voltages during complementary operations of the first group of switching elements or the second group of switching elements connected to both ends of the switching unit.

In addition, a method of driving a multilevel inverter according to another embodiment of the present invention includes driving at least one of a plurality of sub-voltage link units connected to a plurality of voltage sources, respectively, to divide the voltage source into a plurality of voltages; A sub-switching unit comprising a plurality of switching elements respectively connected to both ends of each output of the sub-voltage link unit and an intermediate node dividing the voltage, and a switching unit electrically connected to each other between the adjacent sub-switching units. Outputting a multilevel voltage according to the driving of the switching elements; And periodically changing the polarity of the multilevel voltage during complementary operation of the first group of switching elements or the second group of switching elements connected to both ends of the switching unit.

According to still another aspect of the present invention, there is provided a method of driving a multilevel inverter, the method comprising: receiving a first voltage source, converting the first multilevel voltage into a first multilevel voltage, and outputting the first multilevel voltage; At least one second multilevel inverter receives the first voltage source or at least one second voltage source independent of the first voltage source, converts the output into a second multilevel voltage, and outputs the second multilevel voltage. The method may include outputting a multilevel voltage and a phase different from each other, wherein converting the multilevel voltage and the phase to the first multilevel voltage and outputting the second multilevel voltage to the first multilevel voltage and the phase are different from each other. Dividing the input voltage into at least two voltages; Outputting a multilevel voltage by driving a plurality of switching elements respectively connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage; And periodically changing polarities of the multilevel voltages during complementary operations of the first group of switching elements or the second group of switching elements connected to both ends of the switching unit.

The outputting of the second multilevel voltage and the phase different from the first multilevel voltage may include controlling the switching elements constituting the switching unit, the switching element of the first group, and the switching element of the second group. Characterized in that at least one of the control of the control.

According to an embodiment of the present invention, as the number of output voltage levels increases, the number of switching elements can be significantly reduced, and by reducing the number of elements, the reliability of the system can be improved accordingly, and the manufacturing cost can be significantly reduced. There will be.

In addition, the switching element constituting the H bridge inverter, for example, can reduce the switching loss in synchronization with the fundamental wave frequency of the output voltage.

Furthermore, since only one carrier signal can be used to generate all the control signals for the plurality of switching elements constituting the basic cell of the multilevel inverter, the configuration of the control circuit becomes very easy. For example, according to an exemplary embodiment of the present invention, the system can be operated even when the unit power factor is not different, that is, when the phases of voltage and current are different from each other.

1 is a view showing the structure of a multi-level inverter of the general diode clamping method for obtaining a five-level output voltage,
2 is a view showing the structure of a multilevel inverter according to a first embodiment of the present invention;
3 is a diagram illustrating a method of generating a control signal for controlling the switching unit and the inverter unit of FIG.
4 is a view showing an example of a V _DC / 2 application method of the multi-level inverter of FIG.
FIG. 5 is a view illustrating another example of a method of applying V _DC / 2 of the multilevel inverter of FIG. 2;
6 is a view showing a V _DC application method of the multi-level inverter of FIG.
FIG. 7 is a diagram illustrating a zero voltage applying method of the multilevel inverter of FIG. 2;
8 is a view showing the structure of a multilevel inverter according to a second embodiment of the present invention;
9 is a diagram illustrating a simulation result of the multilevel inverter of FIG. 2;
10 is a diagram illustrating a simulation result of the multilevel inverter of FIG. 8;
11 is a view showing the structure of a multilevel inverter according to a third embodiment of the present invention;
12 is a diagram showing the structure of a multilevel inverter according to a fourth embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

2 is a diagram illustrating a structure of a multilevel inverter according to a first embodiment of the present invention, and FIG. 3 is a diagram illustrating a PWM signal generation method for controlling the switching unit and the inverter unit of FIG. 2.

As shown in FIG. 2, the multilevel inverter according to the first embodiment of the present invention includes a power supply unit (not shown), a voltage link unit 200, a switching unit 210, and some or all of the inverter unit 220. In addition, the control unit 230 for controlling at least one of the switching unit 210 and the inverter unit 220 may be further included.

Here, the power supply may be converted into a DC voltage source such as a solar cell or a commercial power source of AC, such as wind power, to be converted into a DC voltage and output. In FIG. 2, this is briefly represented as voltage source V _DC . The power supply unit may include a rectifying unit for rectifying the input AC power and a smoothing circuit unit for smoothing the voltage output from the rectifying unit to output the DC voltage.

The voltage link unit 200 may include a plurality of capacitors connected in series with each other. At this time, one side and the other side of the plurality of capacitors connected in series with each other are respectively connected to both ends of the voltage source output from the power supply. For example, assuming that the voltage link unit 200 according to the embodiment of the present invention consists of capacitors C ₁ and C ₂ as shown in FIG. 2, capacitors C ₁ and C ₂ are connected in series with each other, and capacitor C ₁ One side of, for example, the positive portion and the other side of the capacitor C ₂ , for example the negative portion, are connected to both ends of the DC voltage source, respectively. The capacitor C ₁ constituting the voltage link unit 200 through this A voltage of V _DC / 2 is applied to both ends of C and C ₂ , respectively. Since such a capacitor may be replaced by a divider resistor, in the embodiment of the present invention, any device may be used as long as the voltage can be divided.

The switching unit 210 includes a plurality of switching elements such as an insulated gate bipolar transistor (IGBT) electrically connected in series with each other. Each of the switching elements positioned at the outermost side of the switching elements connected in series with each other is connected to one side and the other side of the capacitors C ₁ and C ₂ connected in series with each other. Here, the switching elements electrically connected to each other in series may mean that the source terminal of the first switching element and the drain terminal of the second switching element are connected. In addition, the switching unit 210 connects the intermediate point (or second node: N ₂ ) of the switching elements Q ₁ and Q ₂ connected in series to each other to the neutral point (or node 1: N ₁ ) of the capacitors connected in series. .

The switching unit 210 according to the embodiment of the present invention may include, for example, switching elements T ₁ , T ₂ , Q _1, and Q ₂ as shown in FIG. ₂ . At this time, the collector (or drain) terminal of the switching element T ₁ is connected to one side of the capacitor C ₁ and the collector terminal of the switching element T ₂ is connected to the other side of the capacitor C ₂ , respectively. And switching elements emitter of T ₁ (or source) terminal to the collector terminal of the switching element Q _1, the emitter terminal of the switching element Q ₁ is the collector terminal of the switching element Q _2, and the emitter terminal of the switching element Q ₂ Is connected to the collector terminal of the switching element T _{2 so} that the switching elements T ₁ , T ₂ , Q ₁ and Q ₂ are electrically connected in series. In addition, the switching elements Q ₁ and Q ₂ is a connection point that is series-connected to each other (N ₂₎ is to be connected to each other in the capacitor C ₁ and C ₂ connected in series with each other a connection point (N _1).

According to the above configuration, the maximum voltage applied to the switching elements Q ₁ and Q ₂ constituting the switching unit 210 from the voltage link unit 200 is V _DC / 2, and the switching elements T ₁ and T ₂ are the triangle wave signals. Because it is turned on every two cycles, the switching frequency is half the frequency of the triangle wave signal. For example, in order for the maximum voltage to be applied to the switching elements Q ₁ and Q ₂ , the switching unit 210 turns on the switching elements T ₁ and T ₂ under the control of the controller 230, and the switching elements Q ₁ and Q _2. Will be able to turn off. In this case, the maximum voltage that can be output through the output terminal of the switching unit 210 will be V _DC . The detailed operation will be described later.

The inverter unit 220 includes a plurality of switching elements, such as an IGBT, connected to both ends of the output of the switching unit 210 to form at least one topology. In this case, one topology is preferably formed by connecting two switching elements in series, and each switching element may further include a rectifying element connected between the current inlet and the current outlet. In the inverter unit 220 according to the embodiment of the present invention, the switching elements may form a half bridge form or a full bridge form as shown in FIG. 2, and to obtain a three-phase voltage instead of a single phase. Three topological forms could be achieved. In this case, the switching devices forming the half bridge, the full bridge, and the three-phase topology may further be referred to as H-bridges in the exemplary embodiment of the present invention by further including a rectifier connected between the current inlet and the current outlet.

2 shows an H-bridge in the form of a full bridge. In more detail, the switching elements S ₁ and S ₂ are connected in series to each other to form a topology. The collector terminal of the switching element S ₁ is connected to one side of the output terminal of the switching unit 210, that is, the collector terminal of the switching element Q _{1 and} the emitter terminal of the switching element T ₁ , and the emitter terminal of the switching element S ₂ is connected to the switching unit ( The other end of the output terminal 210 is connected to the emitter terminal of the switching element Q ₂ and the collector terminal of the switching element T _{2, and} the emitter terminal of the switching element S ₁ is connected to the collector terminal of the switching element S ₂ . In addition, the switching elements S ₃ and S ₄ form another topology. The collector terminal of the switching device S ₃ is connected to one output terminal of the switching unit 210, an emitter terminal of the switching device S ₄ is connected to the output end the other side of the switching unit 210, the emitter terminal of the switching element S _3, and The collector terminals of the switching element S ₄ are connected to each other. At this time, the contact point of one of the topology the switching elements are connected to each other to form if S ₁ and S ₂ of the connection point (N ₃₎ and the switching element S ₃ and S ₄ also are coupled to each other to form if a topology (N ₄ ), The multilevel voltage is output, and two load points (N ₃ and N ₄ ) may be additionally connected to a load such as a transformer.

According to the above configuration, the maximum applied voltage of the switching element constituting the H-bridge becomes V _DC as mentioned above, and the switching elements of the switching unit 210 and the switching elements constituting the inverter unit 220 are turned on / off. According to the off driving, a voltage having five levels of V _DC , V _DC / 2, 0, -V _DC , and -V _DC / 2 is output through the output terminal Vo of the inverter unit 220. To this end, the multilevel inverter according to the embodiment of the present invention may be divided into four pairs of switching elements that operate complementarily. In other words, in FIG. 2, each switching pair may be composed of switching elements S ₁ , S ₂ , S ₃ , S ₄ , T ₁ , Q ₁ , and T ₂ , Q ₂ . However, the switching combination may vary according to each voltage level, and thus the embodiment of the present invention will not be particularly limited to such a combination. However, it is preferable that the switching elements S ₁ and S ₄ of the inverter unit 220 operate complementarily with S ₂ and S ₃ . In other words, when S ₁ and S ₄ are turned on, S ₂ and S ₃ are turned off, and vice versa.

For example, in the 5-level PWM inverter, the instantaneous voltage modulation index (m _a ) can be obtained by using the instantaneous magnitude of the reference wave (Vref) and the triangular wave amplitude to determine the range of operation modes according to each voltage level. It may be defined as in Equation 1>.

Where Vref is the instantaneous value of the reference voltage and Vc is the peak-peak size of the carrier.

The operation of the multilevel inverter according to the embodiment of the present invention proposed using m _a can be divided into four voltage level operation modes, each of which outputs two voltage levels. The range of each mode as described above and the output voltage of the inverter unit 220 may be expressed as in Equations 2 to 5.

Generating control signals for controlling the switching elements T ₁ , T ₂ , Q ₁ and Q ₂ constituting the switching unit 210 and the switching elements S ₁ to S ₄ of the inverter unit 220. The method can be represented as in FIG.

3 illustrates a PWM technique implemented with one triangle wave to have the same characteristics as the phase inversion arrangement method. For example, when the reference wave (or reference voltage) Vref is greater than zero, the switching elements S ₁ and S ₄ are turned on. If the reference wave is less than zero, the switching elements S ₂ and S ₃ are turned on.

At this time, a method of making a PWM signal for the switching elements of the switching unit 210 is as follows. If the reference wave is between O and Vc (Mode 2) and directly compares to a triangular wave, turn on T ₁ or T ₂ alternately when Vref> Vcarrier and turn off T ₁ and T ₂ when Vref <Vcarrier. . If the reference wave is larger than Vc (Mode 1), the reference wave is subtracted by Vc and compared with the triangular wave. When Vref-Vc &gt; Vcarrier, T ₁ and T ₂ are turned on simultaneously, and when Vref-Vc &lt; Vcarrier, T ₁ or T ₂ are alternately turned off. If the reference wave is less than zero, -Vref is used to invert the phase by 180 degrees to produce a PWM signal. When -Vref is less than Vc (Mode 3), -Vref is directly compared to the triangular wave, and when -Vref is greater than Vc (Mode 4), subtract Vc to -Vref to compare with the triangular wave. If the reference wave is smaller than O, the PWM signal is generated in the same way as when it is larger than zero. Switching elements Q ₁ and Q ₂ operate complementarily to T ₁ and T ₂ .

Operation of the switching elements constituting the switching unit 210 and the inverter unit 220 as described above will be substantially operated by the control of the controller 230. Therefore, the control unit according to the embodiment of the present invention may compare the reference wave and the triangular wave to determine an operation mode according to the comparison result, and operate the switching elements according to the determined mode. Based on this, the controller 230 may include a comparator for comparing the reference wave and the triangular wave, a mode selector for determining an operation mode according to the comparison result, and the controller 230 is further illustrated in the drawings. Although not illustrated, a reference wave generator and a triangular wave generator for generating a reference wave and a triangular wave may be included or may be linked thereto.

One of the important issues in the design of a multilevel inverter as in the embodiment of the present invention is the problem of balancing the voltages of the capacitors constituting the voltage link unit 200. In other words, the voltage across capacitors C ₁ and C ₂ must be equally balanced by V _DC / 2. In an ideal state with no movement of the connection point N ₁ , the voltages of the capacitors C ₁ and C ₂ as well as V _DC / 2. However, substantially, the voltage at the neutral point N ₁ continues to change due to the charging and discharging of C ₁ and C ₂ . If the voltage of the capacitor is not balanced, the output voltage is not symmetrical, resulting in a higher harmonic component of the output current.

In order to solve such a problem, the multilevel inverter according to the embodiment of the present invention needs to appropriately select a switching state. For example, Mode 1 operates to have three switching states as shown in FIGS. 4 to 6, or Mode 2 operates to have three switching states as shown in FIGS. 4, 5, and 7. 4 and 5, when only one DC link switching device is turned on, the output voltages are all V _DC / 2, but the capacitors used may be different. Therefore, in order to balance the voltage of the DC link capacitor constituting the voltage link unit 200, for example, the state of FIGS. 4 and 5 may be alternately used. For example, in Mode 2, the DC link switch, that is, the switching elements T ₁ and T ₂ of the switching unit 210 are alternately turned on, and in Mode 1, they are alternately turned off.

4 to 7, various examples of a driving method of a multilevel inverter according to an exemplary embodiment of the present invention will be described in more detail.

4 is a diagram illustrating an example of a method of applying V _DC / 2 to the multilevel inverter of FIG. 2, and FIG. 5 is a diagram illustrating another example of a method of applying V _DC / 2 to the multilevel inverter of FIG. 2.

First, referring to FIG. 4 together with FIG. 2, the multi-level inverter according to the embodiment of the present invention, as shown in (a) and (b) of FIG. 4, to output a voltage of V _DC / 2. At the same time, the switching elements Q ₁ and T ₂ are turned on and the switching elements S ₁ and S ₄ constituting the inverter unit 220 are turned on. Of course, in this case, the remaining switching elements (T ₁ , Q ₂ , S ₂ , S ₃ ) are turned off. Accordingly, a current path is formed between the capacitor C ₂ constituting the voltage link unit 200 and the output terminal of the inverter unit 220, so that the voltage of V _DC / 2 charged in the capacitor C ₂ is converted to the inverter unit 220. It is output through the output terminal of.

If you want to output a voltage of V _DC / 2 charged to the capacitor C ₁ constituting the voltage link unit 200 is a multi-level inverter according to an embodiment of the present invention as shown in (a) and (b) of FIG. As described above, the switching elements T ₁ and Q ₂ constituting the switching unit 210 may be turned on and the switching elements S ₁ and S ₄ of the inverter unit 220 may be turned on. The remaining switching elements are turned off. As a result, a current path is formed between the capacitor C ₁ constituting the voltage link unit 200 and the output terminal of the inverter unit 220, so that the voltage of V _DC / 2 charged in the capacitor C ₁ is applied to the output terminal of the inverter unit 220. Is output via

Of course, in FIGS. 4 and 5, the switching elements S ₁ and S ₄ of the inverter unit 220 are operated to output a voltage of V _DC / 2. For example, as shown in Table 1 below. In order to output a voltage of -V _DC / 2, the switching elements S ₂ and S ₃ of the inverter unit 220 may be operated or may be controlled to operate complementarily with the switching elements S ₁ and S _{4 at} every step. However, since this is a matter that can be changed as much according to the design intention of the system designer to the last, the embodiment of the present invention will not be limited thereto.

FIG. 6 is a view illustrating a V _DC application method of the multilevel inverter of FIG. 2.

Referring to FIG. 6 together with FIG. 2, the multilevel inverter according to the embodiment of the present invention turns on the switching elements T ₁ and T ₂ constituting the switching unit 210 to apply a voltage of V _DC to the load. At the same time, the switching elements S ₁ and S ₄ constituting the inverter unit 220 are turned on. The remaining switching elements Q ₁ and Q ₂ , and S ₂ and S ₃ are turned off. As a result, a current path is formed between the capacitors C ₁ and C ₂ of the voltage link unit 200 and the output terminal of the inverter unit 220, and V by the sum of the V _DC / 2 voltages charged to the capacitors C ₁ and C ₂ , respectively. _{The DC} voltage is output through the output terminal of the inverter unit 220.

Of course, even in this case, in order to output the -V _DC voltage through the inverter 220, as shown in Table 1 below, the switching elements S ₂ and S ₃ of the inverter unit 220 are turned on and S ₁ and S ₄ are turned on. It may be turned off and may be controlled by the controller to operate the switching elements S ₂ and S ₃ complementary to S ₁ and S _{4 in} every step.

FIG. 7 is a diagram illustrating a zero voltage applying method of the multilevel inverter of FIG. 2.

Referring to FIG. 7 together with FIG. 2, in the multilevel inverter according to the exemplary embodiment of the present invention, the switching elements Q ₁ and Q ₂ constituting the switching unit 210 are turned on and the inverter constituting the inverter 220 is switched on. Turn on elements S ₁ and S ₄ . At this time, the remaining switching elements T ₁ and T ₂ , and S ₂ and S ₃ are turned off. As a result, the current path is interrupted between the capacitors C ₁ and C ₂ of the voltage link unit 200 and the output terminal of the inverter unit 220 so that no voltage charged to the capacitors C ₁ and C ₂ is output through the output terminal. .

Of course, even if the switching elements S ₂ and S ₃ constituting the inverter unit 220 is turned on, since the zero voltage is still output through the output terminal of the inverter unit 220, in the embodiment of the present invention, the switching element to output the zero voltage. It is also possible to turn on S ₁ and S ₄ together or to turn on the switching elements S ₂ and S ₃ . However, even if the voltage is 0, the switching elements S ₁ and S ₄ may be complementary to the switching elements S ₂ and S _{3 at} every stage if the switching elements are deteriorated.

The various driving methods so far can be summarized as shown in <Table 1>. Table 1 shows the levels of the output voltage according to the switching state of the multilevel inverter according to the embodiment of the present invention.

8 is a diagram illustrating the structure of a multilevel inverter according to a second embodiment of the present invention.

As shown in FIG. 8, the multilevel inverter according to the second embodiment of the present invention represents a 9-level inverter, and as in FIG. 2, the voltage link unit 800, the switching unit 810, and the inverter unit ( It may include part or all of the 820, and may further include a controller (not shown).

Here, the voltage link unit 800 constituting the multilevel inverter of FIG. 8 may include a plurality of voltage sub-link units. For example, the first sub-link unit may be in series with each other at the voltage source 1 (V ₁ ). And a first group of capacitors C ₁₁ and C ₁₂ which are connected, and the second sub-link portion includes a second group of capacitors C ₂₁ and C ₂₂ connected in series with each other at voltage source 2 (V ₂ ). It may include.

In addition, the switching unit 810 may include first and second sub-switching units. The first sub-switching part may include switching elements T ₁₁ , Q ₁₁ , Q _12, and T ₁₂ electrically connected in series to each other at both ends of the capacitors C ₁₁ and C ₁₂ constituting the first group, wherein capacitor C ₁₁ And the neutral point of C ₁₂ and the intermediate point of switching elements Q ₁₁ and Q ₁₂ are connected to each other. The second sub-switching part may also include switching elements T ₂₁ , Q ₂₁ , Q ₂₂ and T ₂₂ which are electrically connected in series with each other at capacitors C ₂₁ and C ₂₂ constituting the second group, wherein capacitor C ₂₁ And the neutral point of C ₂₂ and the intermediate point of switching elements Q ₂₁ and Q ₂₂ are connected to each other. Furthermore, the first and second sub-switching parts may be electrically connected to each other. For example, as shown in FIG. 2, the emitter terminal of the switching element Q ₁₂ and the collector terminal of Q ₂₁ may be connected to each other.

In addition, the H-bridge type inverter unit 820 may include four switching elements similar to the inverter unit 220 of FIG. 2. In this case, both ends of the plurality of topologies in which two switching elements are connected in series to each other are connected to both ends of the switching unit 210, respectively. For example, it may be connected to the collector terminal of the switching element Q _{11 and} the emitter terminal of Q ₂₂ which form both ends of the output of the switching unit 810, respectively.

Except for this, the specific connection structure of other individual elements in FIG. 8 is not significantly different from that of the multilevel inverter with reference to FIG.

Briefly looking at the operation process according to the above configuration, the multi-level inverter according to the second embodiment of the present invention can output various levels of voltage according to various on / off operation of the switching elements constituting the switching unit 810 Could be. In other words, when compared to the multilevel inverter of FIG. 2, the multilevel inverter of FIG. 8 is a voltage charged on the capacitors C ₁₁ and C ₁₂ constituting the first group and the capacitors C ₂₁ and C ₂₂ constituting the second group, respectively. By properly adding, the voltage of ± 3 / 2V _{DC and} the voltage of ± 2V _DC can be output more.

For example, in order to apply a voltage of ± 2V _DC to the load through the output terminal of the inverter unit 820, the switching elements T ₁₁ , T ₁₂ , T ₂₁ and T ₂₂ constituting the switching unit 810 are turned on at the same time Q ₁₁ , Q ₁₂ , Q ₂₁ and Q ₂₂ will be turned off. At this time, the switching elements S ₁₁ and S ₁₄ constituting the inverter unit 820 are turned on and the switching elements S ₁₂ and S ₁₃ are turned off, so that a 2V _DC voltage can be output to the load through the output terminal of the inverter unit 820. By turning on the switching elements S ₁₂ and S ₁₃ and simultaneously switching off the switching elements S ₁₁ and S ₁₄ , a voltage of −2 V _DC can be applied to the load. Of course, such an operation is preferably performed under the control of the controller.

The operation of the switching elements constituting the switching unit 810 and the operation of the switching elements constituting the inverter unit 820 to output various levels of voltages have been described above with reference to FIGS. 2 and 8. As it can be fully understood from the above description, further description will be omitted.

FIG. 9 is a diagram illustrating a simulation result of the multilevel inverter of FIG. 2. FIG. 9A illustrates a waveform of an output voltage, and FIG. 9B illustrates a waveform of a current command, an output current, and a grid voltage. . FIG. 10 is a diagram illustrating a simulation result of the multilevel inverter of FIG. 8, and FIG. 10A illustrates a waveform of an output voltage, and FIG. 10B illustrates a waveform of a current command, an output current, and a grid voltage. have.

In this simulation, the PSIM simulation program is used to verify the operating characteristics of the multilevel inverter. <Table 2> is specification of inverter system used for simulation and PI current controller is used.

Rated output

3 kVA
DC link voltage
400 V
Grid voltage

220 Vrms
Line current
13.6 Arms

DC link capacitor

1000 ㎌
Filter inductor
1 mH
Switching frequency

5 ㎑
Grid frequency
60 ㎐

9 illustrates the output voltage, the output current, and the grid voltage when the power factor is 0.707, and the output current is enlarged 10 times to see the phase difference between the grid voltage and the output current.

When the capacitor voltage, the output voltage, and the current waveform of the 9 level inverter shown in FIG. 10 are compared with the output current of the 5 level inverter of FIG. 9, it can be seen that the current waveform of FIG. 10 is closer to the sine wave.

11 is a diagram showing the structure of a multilevel inverter according to a third embodiment of the present invention.

As shown in FIG. 11, the multilevel inverter according to the third embodiment of the present invention has a structure similar to that of the multilevel inverter according to the second embodiment of the present invention with reference to FIG. 8. However, the multilevel inverter of FIG. 11 is a method capable of further extending the output voltage level than the multilevel inverter of FIG. 8.

In other words, the multi-level inverter of FIG. 11 includes a voltage link unit 1100 including capacitors constituting the n-th group corresponding to the voltage source n (Vn), and an n-th sub-coupled with the capacitors constituting the n-th group. And a switching unit 1110 including a switching unit. Of course, in this case, four switching elements of the inverter unit 1120 are the same.

Except for this, the multilevel inverter according to the third embodiment of the present invention is not significantly different from the multilevel inverter referring to FIG. 2 and the multilevel inverter referring to FIG. I would like to.

12 is a diagram showing the structure of a multilevel inverter according to a fourth embodiment of the present invention.

FIG. 12 shows a three-phase five-level inverter formed by installing three topologies on each of three phases, which is an expanded form of the multilevel inverter shown in FIG. 2.

In other words, the multilevel inverter according to the fourth embodiment of the present invention includes a plurality of independent multilevel inverters 1200_1, 1200_2, and 1200_3, and respective multilevel inverters 1200_1, 1200_2, and 1200_3, as shown in FIG. It includes a plurality of transformers (1210_1, 1210_2, 1210_3) are respectively connected as a load to the output terminal of. At this time, one side tap of the secondary side in the transformer 1210_1, 1210_2, 1210_3 becomes a respective voltage output terminal (Va, Vb, Vc), the other side tap is electrically connected to each other.

According to the above configuration, the multilevel inverter according to the fourth embodiment of the present invention has various levels through the respective multilevel inverters 1200_1, 1200_2, and 1200_3, and each multilevel inverter (1200_1, 1200_2, 1200_3). In addition to outputting a voltage having a phase difference therebetween, each of the transformers 1210_1, 1210_2, and 1210_3 may boost and output the voltage.

The connection structure and the driving method of the other individual elements except the above have been described sufficiently through the multi-level inverter with reference to FIG. 2, and the description thereof will be omitted.

While the invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

For example, in the embodiment of the present invention, the switching elements are not limited to the MOS FET, but may be formed of at least one of a junction type FET, a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), a junction gate FET (JFET), and a diode. have. Therefore, the gate of the FET series element or the base of the BJT or IGBT series element may be collectively used as the driving stage of the switching element. In addition, the drain of the FET series device or the collector of the BJT, IGBT series device may be referred to as the current inlet of the switching element, the source of the FET series device and the emitter of the BJT, IGBT series device may be referred to as the current outlet. .

200, 800, 1100: voltage link unit 210, 810, 1110: switching unit
220, 820, 1120: inverter unit 1200_1 to 1200_3: multi-level inverter
1210_1-1210_3: Transformer

Claims (8)

A voltage link unit connected to a plurality of voltage sources, the voltage link unit including a plurality of sub voltage link units for dividing the voltage source into a plurality of voltages;
A sub-switching unit comprising a plurality of switching elements respectively connected to both ends of each output of the sub-voltage link unit and an intermediate node dividing the voltage, and the adjacent sub-switching units are electrically connected to each other; A switching unit for outputting a multilevel voltage according to the driving of the switching elements;
A first group and a second group of switching elements connected to both ends of the output of the switching unit, and periodically complementary to the polarity of the multilevel voltage during complementary operation of the first group of switching elements or the second group of switching elements. Inverter unit to change and output
Multi-level inverter comprising a. The method of claim 1,
The plurality of switching elements connected to the output terminal of the switching unit is a multi-level inverter, characterized in that the adjacent switching elements are connected to each other in series form. The method of claim 1,
And the voltage link unit outputs a 9 level voltage having different polarities when the voltage link unit has two sub voltage link units that divide the corresponding voltage source into two voltages. A first multilevel inverter receiving a first voltage source and converting the first voltage source into a first multilevel voltage; And
Receives the first voltage source or at least one second voltage source independent of the first voltage source, converts the second voltage into a second multilevel voltage, and outputs the second multilevel voltage differently from the first multilevel voltage; At least one second multilevel inverter,
The first multilevel inverter and the second multilevel inverter,
A voltage link unit dividing an input voltage into at least two voltages;
A switching unit including a plurality of switching elements connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage, and outputting a multilevel voltage according to driving of the switching elements; And
And switching devices of the first group and the second group connected to both ends of the switching unit, and periodically changing the polarity of the multilevel voltage during complementary operation of the switching device of the first group or the switching device of the second group. Inverter output
Multi-level inverter comprising a. 5. The method of claim 4,
At least one of the first multilevel inverter and the second multilevel inverter may include a controller configured to output a multilevel voltage having a different phase according to control of at least one of the switching unit and the inverter unit. Multilevel Inverter. Driving at least one of a plurality of sub voltage link units connected to a plurality of voltage sources, respectively, to divide the voltage source into a plurality of voltages;
And a sub switching unit including a plurality of switching elements respectively connected to both ends of each output of the sub voltage link unit and an intermediate node dividing the voltage, and a switching unit electrically connected to each other between adjacent sub switching units. Outputting a multilevel voltage according to the driving of the switching elements;
Periodically changing the polarity of the multilevel voltage during the complementary operation of the first group of switching elements or the second group of switching elements connected to both ends of the switching unit
A method of driving a multilevel inverter, characterized in that it comprises a. Receiving, by the first multilevel inverter, a first voltage source and converting the first multilevel voltage into a first multilevel voltage;
At least one second multilevel inverter receives the first voltage source or at least one second voltage source independent of the first voltage source, converts the output into a second multilevel voltage, and outputs the second multilevel voltage. Outputting different levels of multilevel voltage and phase,
The converting into the first multilevel voltage and outputting the second multilevel voltage out of phase with the first multilevel voltage may include:
Dividing a voltage inputted by a voltage link unit connected to a voltage source into at least two voltages;
Outputting a multilevel voltage by driving a plurality of switching elements respectively connected to both ends of an output of the voltage link unit and an intermediate node dividing the voltage; And
Periodically changing the polarity of the multilevel voltage during the complementary operation of the switching device of the first group or the switching device of the second group connected to both ends of the switching unit including the plurality of switching devices.
A method of driving a multilevel inverter, characterized in that it comprises a. The method of claim 7, wherein
The step of outputting the second multilevel voltage different from the phase of the first multilevel voltage may include controlling the switching elements constituting the switching unit, switching the first group of switching elements, and the second group of switching elements. A method of driving a multilevel inverter, characterized in that made by at least one of the control.

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